scholarly journals The Robustness of Synthetic Observations in Producing Observed Core Properties: Predictions for the TolTEC Clouds to Cores Legacy Survey

2021 ◽  
Vol 923 (1) ◽  
pp. 25
Author(s):  
S. K. Betti ◽  
R. Gutermuth ◽  
S. Offner ◽  
G. Wilson ◽  
A. Sokol ◽  
...  
Keyword(s):  
Column Density ◽  
Structure Change ◽  
Young Stellar Objects ◽  
Analysis Framework ◽  
Stellar Objects ◽  
Star Forming ◽  
Stellar Feedback ◽  
Mass Size ◽  
Hydrodynamical Simulations ◽  
Cloud Evolution

Abstract We use hydrodynamical simulations of star-forming gas with stellar feedback and sink particles—proxies for young stellar objects (YSOs)—to produce and analyze synthetic 1.1 mm continuum observations at different distances (150–1000 pc) and ages (0.49–1.27 Myr). We characterize how the inferred core properties, including mass, size, and clustering with respect to diffuse natal gas structure, change with distance, cloud evolution, and the presence of YSOs. We find that atmospheric filtering and core segmentation treatments have distance-dependent impacts on the resulting core properties for d < 300 pc and 500 pc, respectively, which dominate over evolutionary differences. Concentrating on synthetic observations at further distances (650–1000 pc), we find a growing separation between the inferred sizes and masses of cores with and without YSOs in the simulations, which is not seen in recent observations of the Monoceros R2 (Mon R2) cloud at 860 pc. We find that the synthetic cores cluster in smaller groups, and that their mass densities are correlated with gas column density over a much narrower range, than those in the Mon R2 observations. Such differences limit the applicability of the evolutionary predictions we report here, but will motivate our future efforts to adapt our synthetic observation and analysis framework to next generation simulations, such as Star Formation in Gaseous Environments (STARFORGE). These predictions and systematic characterizations will help to guide the analysis of cores on the upcoming TolTEC Clouds to Cores Legacy Survey on the Large Millimeter Telescope Alfonso Serrano.

scholarly journals Chemical Compositions in the Vicinity of Protostars in Ophiuchus

2021 ◽  
Vol 922 (2) ◽  
pp. 152
Author(s):  
Kotomi Taniguchi ◽  
Liton Majumdar ◽  
Adele Plunkett ◽  
Shigehisa Takakuwa ◽  
Dariusz C. Lis ◽  
...  
Keyword(s):  
Column Density ◽  
Density Ratio ◽  
Young Stellar Objects ◽  
Chemical Compositions ◽  
Stellar Objects ◽  
Star Forming ◽  
Molecular Lines ◽  
Be Star ◽  
The Difference ◽  
Density Ratios

Abstract We have analyzed Atacama Large Millimeter/submillimeter Array Cycle 4 Band 6 data toward two young stellar objects (YSOs), Oph-emb5 and Oph-emb9, in the Ophiuchus star-forming region. The YSO Oph-emb5 is located in a relatively quiescent region, whereas Oph-emb9 is irradiated by a nearby bright Herbig Be star. Molecular lines from cyclic-C3H2 (c-C3H2), H2CO, CH3OH, 13CO, C18O, and DCO+ have been detected from both sources, while DCN is detected only in Oph-emb9. Around Oph-emb5, c-C3H2 is enhanced at the west side, relative to the IR source, whereas H2CO and CH3OH are abundant at the east side. In the field of Oph-emb9, moment 0 maps of the c-C3H2 lines show a peak at the eastern edge of the field of view, which is irradiated by the Herbig Be star. Moment 0 maps of CH3OH and H2CO show peaks farther from the bright star. We derive the N(c-C3H2)/N(CH3OH) column density ratios at the peak positions of c-C3H2 and CH3OH near each YSO, which are identified based on their moment 0 maps. The N(c-C3H2)/N(CH3OH) ratio at the c-C3H2 peak is significantly higher than at the CH3OH peak by a factor of ∼19 in Oph-emb9, while the difference in this column density ratio between these two positions is a factor of ∼2.6 in Oph-emb5. These differences are attributed to the efficiency of the photon-dominated region chemistry in Oph-emb9. The higher DCO+ column density and the detection of DCN in Oph-emb9 are also discussed in the context of UV irradiation flux.

scholarly journals Hα emission-line stars in molecular clouds

2019 ◽  
Vol 630 ◽  
pp. A90 ◽  
Author(s):  
Bertil Pettersson ◽  
Bo Reipurth
Keyword(s):  
Molecular Clouds ◽  
Young Stellar Objects ◽  
Be Stars ◽  
Stellar Objects ◽  
Strong Concentration ◽  
Ob Stars ◽  
Star Forming ◽  
Hα Emission ◽  
Objective Prism ◽  
Emission Stars

A deep objective-prism survey for Hα emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Hα emitters were detected, 353 of which are new detections. There is a strong concentration of these Hα emitters towards the molecular clouds surrounding the CMa OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of Hα emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the Hα emitters are detected by WISE, of which 75% was detected with usable photometry. When plotted in a WISE colour–colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Hα emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the Hα stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the Hα stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

scholarly journals Variability of young stellar objects in the star-forming region Pelican Nebula

2019 ◽  
Vol 627 ◽  
pp. A135 ◽  
Author(s):  
A. Bhardwaj ◽  
N. Panwar ◽  
G. J. Herczeg ◽  
W. P. Chen ◽  
H. P. Singh
Keyword(s):  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Main Sequence Stars ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Optical Wavelengths

Context. Pre-main-sequence variability characteristics can be used to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. The photometric variability of pre-main-sequence stars is studied at optical wavelengths to explore star–disk interactions, accretion, spots, and other physical mechanisms associated with young stellar objects. Methods. We observed a field of 16′ × 16′ in the star-forming region Pelican Nebula (IC 5070) at BVRI wavelengths for 90 nights spread over one year in 2012−2013. More than 250 epochs in the VRI bands are used to identify and classify variables up to V ∼ 21 mag. Their physical association with the cluster IC 5070 is established based on the parallaxes and proper motions from the Gaia second data release (DR2). Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalog of optical time-series photometry with periods, mean magnitudes, and classifications for 95 variable stars including 67 pre-main-sequence variables towards star-forming region IC 5070. The pre-main-sequence variables are further classified as candidate classical T Tauri and weak-line T Tauri stars based on their light curve variations and the locations on the color-color and color-magnitude diagrams using optical and infrared data together with Gaia DR2 astrometry. Classical T Tauri stars display variability amplitudes up to three times the maximum fluctuation in disk-free weak-line T Tauri stars, which show strong periodic variations. Short-term variability is missed in our photometry within single nights. Several classical T Tauri stars display long-lasting (≥10 days) single or multiple fading and brightening events of up to two magnitudes at optical wavelengths. The typical mass and age of the pre-main-sequence variables from the isochrone fitting and spectral energy distributions are estimated to be ≤1 M⊙ and ∼2 Myr, respectively. We do not find any correlation between the optical amplitudes or periods with the physical parameters (mass and age) of pre-main-sequence stars. Conclusions. The low-mass pre-main-sequence stars in the Pelican Nebula region display distinct variability and color trends and nearly 30% of the variables exhibit strong periodic signatures attributed to cold spot modulations. In the case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable on a timescale of one year.

scholarly journals Far-IR Spectrophotometry of HH Flows with the ISO Long-Wavelength Spectrometer

1997 ◽  
Vol 182 ◽  
pp. 111-120
Author(s):  
R. Liseau ◽  
T. Giannini ◽  
B. Nisini ◽  
P. Saraceno ◽  
L. Spinoglio ◽  
...  
Keyword(s):  
Mass Loss ◽  
Line Emission ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Shock Models ◽  
Ir Spectrophotometry ◽  
Hh Objects ◽  
Loss Rates

Full Iso-Lws spectral scans between about 45 to 190 μm of 17 individual HH objects in 7 star forming regions have revealed essentially only [O I] 63 μm line emission, implying that the Fircooling of these objects is totally dominated by this line alone. In this case, J-shock models can be used to determine the mass loss rates of the HH exciting sources. These mass loss rates are in reasonably good agreement with those estimated for the accompanying CO flows, providing first observational evidence that HH and molecular flows are driven by the same agent. The Lmech – Lbol relation, based on our results with the Lws, implies that young stellar objects of lower mass are loosing mass at relatively higher rates than their more massive counterparts.

scholarly journals Identification of Young Stellar Object candidates in the Gaia DR2 x AllWISE catalogue with machine learning methods

2019 ◽  
Vol 487 (2) ◽  
pp. 2522-2537 ◽  
Author(s):  
G Marton ◽  
P Ábrahám ◽  
E Szegedi-Elek ◽  
J Varga ◽  
M Kun ◽  
...  
Keyword(s):  
Machine Learning ◽  
3D Structure ◽  
Physical Nature ◽  
Machine Learning Techniques ◽  
Young Stellar Objects ◽  
Support Vector ◽  
Wide Field ◽  
Stellar Objects ◽  
Star Forming ◽  
Gaia Dr2

ABSTRACT The second Gaia Data Release (DR2) contains astrometric and photometric data for more than 1.6 billion objects with mean Gaia G magnitude &lt;20.7, including many Young Stellar Objects (YSOs) in different evolutionary stages. In order to explore the YSO population of the Milky Way, we combined the Gaia DR2 data base with Wide-field Infrared Survey Explorer (WISE) and Planck measurements and made an all-sky probabilistic catalogue of YSOs using machine learning techniques, such as Support Vector Machines, Random Forests, or Neural Networks. Our input catalogue contains 103 million objects from the DR2xAllWISE cross-match table. We classified each object into four main classes: YSOs, extragalactic objects, main-sequence stars, and evolved stars. At a 90 per cent probability threshold, we identified 1 129 295 YSO candidates. To demonstrate the quality and potential of our YSO catalogue, here we present two applications of it. (1) We explore the 3D structure of the Orion A star-forming complex and show that the spatial distribution of the YSOs classified by our procedure is in agreement with recent results from the literature. (2) We use our catalogue to classify published Gaia Science Alerts. As Gaia measures the sources at multiple epochs, it can efficiently discover transient events, including sudden brightness changes of YSOs caused by dynamic processes of their circumstellar disc. However, in many cases the physical nature of the published alert sources are not known. A cross-check with our new catalogue shows that about 30 per cent more of the published Gaia alerts can most likely be attributed to YSO activity. The catalogue can be also useful to identify YSOs among future Gaia alerts.

scholarly journals Physical Properties of Molecular Envelopes in Low-Mass Star-Forming Regions

2000 ◽  
Vol 197 ◽  
pp. 61-70
Author(s):  
Nagayoshi Ohashi
Keyword(s):  
Physical Properties ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Narrow Line ◽  
Stellar Objects ◽  
Velocity Pattern ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Line Widths

We have carried out interferometric observations of pre-protostellar and protostellar envelopes in Taurus. Protostellar envelopes are dense gaseous condensations with young stellar objects or protostars, while pre-protostellar envelopes are those without any known young stellar objects. Five pre-protostellar envelopes have been observed in CCS JN=32–21, showing flattened and clumpy structures of the envelopes. The observed CCS spectra show moderately narrow line widths, ~0.1 to ~0.35 km s–1. One pre-protostellar envelope, L1544, shows a remarkable velocity pattern, which can be explained in terms of infall and rotation. Our C18O J=1–0 observations of 8 protostellar envelopes show that they have also flattened structures like pre-protostellar envelopes but no clumpy structures. Four out the eight envelopes show velocity patterns that can be explained by motions of infall (and rotation). Physical properties of pre-protostellar and protostellar envelopes are discussed in detail.

scholarly journals Abundant, hot water toward young stellar objects

1997 ◽  
Vol 178 ◽  
pp. 397-400
Author(s):  
F.P. Helmich ◽  
E.F. Van Dishoeck ◽  
J.H. Black ◽  
Th. De Graauw
Keyword(s):  
Hot Water ◽  
Resolving Power ◽  
Young Stellar Objects ◽  
Small Scale ◽  
Interstellar Space ◽  
Infrared Space Observatory ◽  
Direct Estimate ◽  
Infrared Source ◽  
Stellar Objects ◽  
Star Forming

The large amount of water vapour in the Earth's atmosphere makes it extremely difficult to observe water in interstellar space, except under unusual conditions (e.g., masers). The Short Wavelength Spectrometer (SWS; de Graauw et al. 1996) on board the Infrared Space Observatory (ISO) provides an unique opportunity to study the ro-vibrational fundamental bands of water in absorption against bright infrared continuum sources. Such absorption line data have several advantages over emission observations. For example, only a pencil beam to the infrared source is probed, which minimizes the complications due to the small-scale physical and chemical heterogeneity of star-forming regions. In addition, lines from all rotational levels are present within a vibrational band, so that the complete spectrum yields a direct estimate of the level populations and excitation temperature along the line of sight. Other molecules, such as CO, HCN and C2H2, can be observed with the same technique, leading to accurate relative abundances. The main limitation of the ISO-SWS grating is its low spectral resolving power, λ/Δ λ ≈ 1350 at 6 μm, since the lines are intrinsically much narrower. This limits the sensitivity, so that only high column densities can be detected, and complicates the interpretation because detectable lines are often saturated. The low spectral resolution also blends the lines, making it difficult to determine the equivalent widths unambiguously. The ISO-SWS is therefore particularly sensitive to molecules in warm gas with relatively large line widths (Δ V > 3 km s−1).

scholarly journals Preliminary observations of water masers associated with IRAS4A and IRAS4B

2002 ◽  
Vol 206 ◽  
pp. 63-67 ◽  
Author(s):  
Kevin B. Marvel ◽  
Mark Claussen ◽  
Alwyn Wootten
Keyword(s):  
Proper Motion ◽  
Position Angle ◽  
Young Stellar Objects ◽  
Linear Features ◽  
Stellar Objects ◽  
Star Forming ◽  
Water Masers

We present preliminary observations of water masers associated with IRAS4, a pair of young stellar objects in the NGC 1333 star forming region. The masers are quite strong and spatially distinct. Proper motion observations have been obtained from various epochs of observation typically separated by about three weeks. IRAS4A consists of two regions of maser activity separated by about 114 AU along a position angle of 138 degrees. Expansion of about 68 km/s is detected. IRAS4B consists of two linear emission regions separated by about 175 AU on a 150 degree position angle. The linear features are about 15 AU in length and about 2 AU thick. They are expanding away from each other at about 70 km/s.

Magnetic Fields and Disks in Star-forming Regions

1993 ◽  
Vol 10 (3) ◽  
pp. 247-249 ◽  
Author(s):  
C.M. Wright ◽  
D.K. Aitken ◽  
C.H. Smith ◽  
P.F. Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Transverse Component ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Molecular Outflow ◽  
The Magnetic Field

AbstractThe star-formation process is an outstanding and largely unsolved problem in astrophysics. The role of magnetic fields is unclear but is widely considered to be important at all stages of protostellar evolution, from cloud collapse to ZAMS. For example, in some hydromagnetic models, the field may assist in removing angular momentum, thereby driving accretion and perhaps bipolar outflows.Spectropolarimetry between 8 and 13μm provides information on the direction of the transverse component of a magnetic field through the alignment of dust grains. We present results of 8–13μm spectropolarimetric observations of a number of bipolar molecular outflow sources, and compare the field directions observed with the axes of the outflows and putative disk-like structures observed to be associated with some of the objects. There is a strong correlation, though so far with limited statistics, between the magnetic field and disk orientations. We compare our results with magnetic field configurations predicted by current models for hydromagnetically driven winds from the disks around Young Stellar Objects (YSOs). Our results appear to argue against the Pudritz and Norman model and instead seem to support the Uchida and Shibata model.

scholarly journals GAMMA-RAY EMISSION FROM MASSIVE STAR FORMING REGIONS

2008 ◽  
Vol 17 (10) ◽  
pp. 1889-1894 ◽  
Author(s):  
A. T. ARAUDO ◽  
G. E. ROMERO ◽  
V. BOSCH-RAMON ◽  
J. M. PAREDES
Keyword(s):  
Gamma Ray ◽  
Surrounding Medium ◽  
Strong Shock ◽  
High Energy ◽  
Young Stellar Objects ◽  
Present Contribution ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Impact

Recent radio observations support a picture for star formation where there is accretion of matter onto a central protostar with the ejection of molecular outflows that can affect the surrounding medium. The impact of a supersonic outflow on the ambient gas can produce a strong shock that could accelerate particles up to relativistic energies. Strong evidence for this has been the detection of nonthermal radio emission coming from the jet termination region of some young massive stars. In the present contribution, we study the possible high-energy emission due to the interaction of relativistic particles, electrons and protons, with the magnetic, photon and matter fields inside a giant molecular cloud. Electrons lose energy via relativistic Bremsstrahlung, synchrotron radiation and inverse Compton interactions, and protons cool mainly through inelastic collisions with atoms in the cloud. We conclude that some massive young stellar objects (YSOs) might be detectable at gamma-rays by next generation instruments, both satellite-borne and ground based.

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